This invention relates generally to a vehicle steering apparatus and more specifically to a power steering apparatus in which, as vehicle speed increases, the feel of the steering apparatus approximates the feel of a non-power assisted steering apparatus.
Many known vehicle power steering systems reduce the effort required to turn the steering wheel of a vehicle during parking and low speed maneuvers. In order to maximize the operator's feel of control over the vehicle during high speed operation, attempts have been made to increase the effort required to turn the steering wheel at high speeds so that the power steering system tends to approximate the feel of a non-power assisted steering system. Thus, U.S. Pat. No. 4,119,172 discloses a power steering system in which, at high speeds, an electrically actuated valve reduces the fluid pressure delivered to a steering control valve. This results in a reduction in the power-assist at relatively high vehicle speeds. Since the fluid pressure being delivered to the power steering valve is being reduced, there is a danger that an adequate supply of fluid may not be quickly available for emergency steering manuevers. Other patents disclosing the concept of providing higher steering effort at increased speeds are U.S. Pat. Nos. 2,791,287; 3,744,515; 3,902,320; and 4,000,785.